# [ODE] Iterative solution

Antonio_Martini@scee.net Antonio_Martini at scee.net
Mon Mar 17 03:19:01 2003

```>I'm going to look into solving one constraint at a time (as opposed to
>one joint at a time). If it works, I think the LCP solver becomes
>solving a single variable equation, but I could be wrong...
i think that probably might not make it much better.
There is an ideal(problem depedent) matrix size where the O(n^3)
is not significant anymore and splitting the matrix further would just
increase the number of iterations making the general solution slower.
Maximum performances
may not be in the 'maximum splitting' strategy of the LCP matrix but rather
in
a balance between relaxation an sub matrices size. Solving constraints
directly decreases
the number of iterations needed and as long as the matrix is small the
O(n^3)
complexity doesn't matter that much.

Antonio

<david@csworkbench.com>@q12.org on 17/03/2003 09:46:21

To:    <ode@q12.org>
cc:
Subject:    Re: [ODE] Iterative solution

I'm going to look into solving one constraint at a time (as opposed to
one joint at a time). If it works, I think the LCP solver becomes
solving a single variable equation, but I could be wrong.....  If you
know for sure, let me know.  I'm spending over 80% of my time making the
(up to) 6x6 system matrix and solving it, so anything that can be done
to speed those steps up would help.  I'd like to go back to the Cholesky
solver, but it ceased to work ("A is not positive definite"????) when I
took the Jacobian calculations out of the iteration loop.  It would
really help to figure out why that is happening.

David Whittaker

> Have you tried the iterative method on something like box-stacking?
> How does it compare to the regular solver on that?
>
> cheers,
> m
>
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> ODE@q12.org
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